Recent developments, such as e-commerce or an increasingly desired individualisation of products, require the introduction of complex material flow systems, in particular to be able to meet the demands of the intralogistics sector which have increased as a result. Therefore, material flow systems are desirable which can be adapted as flexibly as possible to changing conditions, without thereby losing efficiency. Fundamental tasks which should be performed by material flow systems of this type in the intralogistics sector include, in particular, the transportation, assembly, sorting, and intermediate storage of goods packages. So-called “plug-and-work” material flow systems are used, in particular, those which have a decentralised control of the individual modules in order to allow as flexible an adaptation as possible of the material flow system to changing conditions.
A material flow system of this type is the so-called “FlexConveyor” which is known, for example, from DE 10 2008 059 529 A1. It comprises a material flow system which is controllable in a decentralised manner and has a plurality of preferably identical modules for the transportation of goods packages, the individual modules being easily assembled and detached from one another to thus be able to provide a material flow system which meets the respective requirements. The material flow system described in the mentioned document allows the transportation of goods packages by transport steps along a material flow path, from a starting module to a target module. Here, any module of the material flow system can be used as the starting module or as the target module, so that under a decentralised control, the proposed material flow system can perform complex transportation tasks involving a plurality of goods packages which can be conveyed from various starting modules to different target modules. Further material flow systems are disclosed in DE 10 2009 031 137 A1 and in DE 10 2009 033 600 A1.
Zaezilia Seibold, Thomas Stoll and Kai Furmans, Layout-optimized sorting of goods with decentralized controlled conveyor modules, Systems Conference (SysCon), 2013, IEEE International, p. 628-633, 2013, describes, in addition to the above-mentioned “FlexConveyor,” a further material flow system, also known as a “GridSorter.” The so-called “GridSorter” comprises, in particular, an area, which is as cohesive as possible, of modules which are preferably arranged in a rectangular shape. Since, by virtue of this arrangement, the size and shape of the material flow system as well as the positions of starting modules and target modules can be freely selected within wide limits, this device has a high degree of flexibility so that it can adapt to the respective demands and general conditions of its use, particularly in the intralogistics sector.
The “GridSorter” has a continuous process, running in the background, of independent layout detection, which is particularly configured to detect possible changes in layout, for example due to the breakdown of individual modules.
In addition to preventing collisions between different goods packages which are transported at the same time in the material flow system, a control means in the material flow system should be configured in such a way to prevent so-called “deadlocks.” The term “deadlock” in this context can describe a state of a goods package in which said goods package is within a loop in the material flow system and therefore cannot arrive at the desired target module. According to Stephan H. Mayer, in Development of a completely decentralized control system for modular continuous conveyors, Wissenschaftliche Berichte des Institutes für Fördertechnik and Logistiksysteme der Universitat Karlsruhe (TH), Vol. 73, Editor Prof. Dr. Ing. Kai Furmans, Universitätsverlag Karlsruhe, 2009, chapter 4.2.3, pages 69-75, the risk of deadlocks can be reduced by reserving the entire material flow path from the starting module to the target module before the goods package is actually transported in the associated material flow system.
This dissertation investigates the extent to which a discrete reservation of modules can be advantageous. In this case, each module involved would only be reserved for a particular time frame in which the arrival of the goods package was expected. Here, a deadlock situation could be avoided in that one reservation in each case for all involved modules from the starting module to the target module could be made in each case for particular time frames. However, the author does not pursue this approach further, because he assumes that in the event that a plurality of goods packages is simultaneously present in the material flow system, he estimates that it is very likely that the expected arrival times cannot be guaranteed due to mutual obstructions of the goods packages at interfaces and therefore the time frames would always have to be moved. In particular, to avoid deadlock situations, he assumes that the modules would be forced to permanently adapt their time frames to the actual arrival times and accordingly to update the reservations which have already been made. This would significantly increase the expense in terms of calculation time and data transmission which is required for this purpose, as a result of which he fears that substantial restrictions would arise in the scalability of the material flow system which is controlled in this way.
In the intralogistics sector, so-called shuttle storage systems have been used to an increasing extent for some years which make it possible to achieve an increased throughput, compared to conventional automated storage systems which have one stacker crane per storage aisle. In the shuttle stores, the individual vehicles (shuttles) can move on defined pathways (material flow paths). A shuttle (vehicle) can change the predefined pathway (storage aisle, material flow path) or not, depending on the configuration. The vehicles (shuttles) either remain in a storage aisle or on storage racking levels (material flow path) or they can change the racking levels by means of a mechanical device, for example a lift. The efficiency of a storage system increases with the number of vehicles (shuttles), provided that the control means ensures that as few waiting times as possible and/or that no deadlocks occur as a result. The following publication Rotgeri M, Dieckerhoff M, ten Hompel M (2014), Vergleich von additiv and herkömmlich gefertigten Strukturen für ein neuartiges Regalfahrzeug, Logistics Journal: Proceedings, Vol. 2014, discloses a novel storage and retrieval vehicle which can also automatically change the racking levels. Formed in the storage aisle is a close network of defined paths on which vehicles can move as required. A control means for the routing of a shuttle storage system of this type does not form part of the article. A decentralised control concept for an electric monorail conveyor is disclosed by Chisu, Razvan, Florian Kuzmany, and Willibald A. Günthner in “Realisierung einer agentenbasierten Steuerung für Elektrohängebahnsysteme” Internet der Dinge in der Intralogistik. Springer Berlin Heidelberg, 2010. 263-274. Common to these electric monorail conveyor systems and a shuttle storage system is the fact that that they are track-guided. However, the route network is not as close as in the described shuttle storage system. The publication “Wandelbare automatisierte Materialflusssysteme für dynamische Produktionsstrukturen”, Fördertechnik—Materialfluss—Logistik, Wilke, Michael (2006) discloses a control means of a system in which the vehicles can automatically make route reservations which they store in a central area which can be accessed by all vehicles. Deadlocks due to circular layouts are not considered further because they do not occur with the considered number of vehicles and with the type of route network.